Medical care is performed inside a blood vessel depending on a highly functional catheter such as a balloon catheter, a stent and the like. For this medical care, it has been becoming popular to use an imaging apparatus for diagnosis such as an optical coherence tomography (OCT) apparatus and the like for a diagnosis before operation or a follow-up confirmation after operation.
This imaging apparatus for diagnosis includes an optical lens at the distal end and further, includes a catheter installed with an optical fiber attached with an optical mirror. Then, a radial scan is carried out by inserting the catheter thereof inside a blood vessel of a patient, by illuminating light onto the blood vessel wall through the optical mirror while rotating the optical mirror and by light-receiving the reflected light again from a biological tissue through the optical mirror thereof, and a cross-sectional image of the blood vessel is to be constructed based on the obtained reflected light. Also, for an improved type OCT apparatus, there has been developed an optical frequency domain imaging (OFDI) apparatus.
The basic principle of the optical coherence tomographic diagnostic apparatus lies in that the light outputted from a light source inside the apparatus is divided into a measurement light and a reference light, and the measurement light is emanated through the optical mirror of the abovementioned optical fiber. Then, a scattering light reflected by the biological tissue is light-received through the same optical fiber, there is obtained an interference light with respect to the reference light which is reflected by going through a known distance, a tomographic image of the biological tissue (blood vessel) in the vicinity of the catheter is to be obtained from the intensity thereof. An example is disclosed in Japanese unexamined patent publication No. 2007-267867.
In particular, in case of the optical frequency domain imaging apparatus, it is possible, by sweeping the emanated optical wavelength repeatedly within a predetermined range, to obtain reflection-intensity distribution in the depth direction, in which the measurement light and the reference light are referenced to a same point, from the frequency distribution of the interference light obtained without handling the optical path length of the reference light.